The present invention relates to a matrix display device, and more particularly to a device for displaying an image in plural tones in response to an analog image signal.
In recent years, matrix display devices including a liquid crystal display, a plasma display, an EL (electroluminescence), etc. have been developed as display devices in place of CRT display devices.
The display screen of the matrix display device has plural X signal lines arranged in a horizontal (X) direction of the screen, and plural Y signal lines in a vertical (Y) direction thereof; each of picture cells (pixels) is displayed at each of intersecting points of the X and Y signal lines. The X signal lines are supplied with image signals (luminance or color signals), whereas the Y signal lines are supplied with selective signals for scanning lines.
Several techniques of the display for the matrix display device, which can make the display with multi-color and multi-tone as in the CRT display device, have been developed. For example, in the liquid crystal matrix display device, different tones can be exhibited in terms of different integration values of transmission light beams for liquid crystal cells. The different integration values of transmission light beams can be exhibited by thinning out image signals for each frame of image display, or pulse-width modulating the image signals supplied to the X signals. In these techniques, the difference in time-integration values of image signals are converted into different tones. On the other hand, if the liquid crystal devices which continuously vary in their transmissivity in accordance with varying applied voltages is used, it is possible to exhibit the tone by controlling the applied voltage.
JP-A-62-195628 filed on Jan. 13, 1986 by HITACHI, LTD. in Japan discloses a liquid crystal display device which provides monochrome or 8 (eight)color display in accordance with input signals which are binary digital signals. JP-A-61-75322 filed on Sep. 20, 1984 by FUJITSU GENERAL Co. Ltd. discloses a system which provides tone display by changing signal levels between adjacent fields. JP-A-59-78395 filed Oct. 27, 1982 by SUWA SEIKOSHA Co. Ltd. discloses a multi-tone display system using pulse-width modulation.
Now referring to FIGS. 1 and 2, the operation of a liquid crystal matrix display device which does not have the function of tone display will be explained. An input signal for this matrix display device is a binary digital signal represented by the value of "0" or "1".
In FIG. 1, 1 is a liquid crystal display device (or liquid crystal display module, hereinafter referred to as LCM) provided with a matrix shape liquid crystal panel 17 the pixels of which are selected by X signal lines and Y signal lines. 18 is display data in which display ON (white) is represented by "1" and display OFF (black) is represented by "0". 3 is a latch clock in synchronism with the display data 18. 4 is a horizontal clock indicative of the period during which the amount of display data corresponding to one horizontal display is sent. 5 is a head line signal. 19 is a voltage generating section. 20 is a display ON voltage. 21 is a display OFF voltage. 13 is a selected voltage. 14 is a non-selected voltage. These voltages are generated by the voltage generating section. 22 is an X driving section for driving X-signal lines which is reset by the trailing edge of the horizontal clock, takes in the display data 18 corresponding to one horizontal display, converts the data into a display ON voltage for the data "1" and into a display OFF voltage for the data "0", and finally outputs the converted voltage in accordance with the next trailing edge of the horizontal clock 4. X1-X640 are panel data which are output voltages from the X driving section. 16 is a Y driving section for driving Y signal lines. Y1-Y200 are scanning signals. The Y driving section 16 takes in the head line signal in accordance with the trailing edge of the horizontal clock 4, initially takes the scanning signal Y1 as the selected voltage 13, and shifts the selected voltage 13 in the order of scanning signals Y2, Y3, . . . Y200 (each of the scanning signals other than the scanning signal which is a selected voltage 13 is a non-selected voltage 14). The liquid crystal panel 17 displays data on the line corresponding to the scanning signal Y1 which is at the level of the selected voltage in accordance with the panel data X1-X640 which are X-signal-line driving voltages X1-X640 generated from the X driving section 22.
FIG. 2 is a timing chart for explaining the operation of the LCM 1.
In FIG. 1, the X driving section 22 successively takes in the display data for each one line in synchronism with the latch clock 3 and in accordance with the subsequent horizontal clock 4, outputs as panel data X1-X640, the display ON voltage 20 or the display OFF voltage selected by "1" or "0" of each data. As shown in FIG. 2, therefore, the X driving section 22 outputs the voltage selected by the data for a 200-th line which is a last line while taking in a first line data, and outputs the voltage selected by the first line data while taking in a second line data. Namely, the output of display data lags by one line from the take-in thereof. Then, in order that the scanning signal on the line to be output by the X driving section 22 is the selected voltage, the Y driving section 16 takes in the head line signal 5 at the timing of the horizontal clock 4, takes the scanning signal Y1 as the selected voltage 13 and thereafter shifts the selected voltage 13 in accordance with the horizontal clock 4. In accordance with the voltage of each of the panel data X1-X640, the display panel 17 displays "white", on the line corresponding to the scanning line which is the selected voltage, when it is the display ON voltage and displays "black" when it is the display OFF data.
Color display (8 color display) can be made by arranging color filters of red, green and blue in the direction of lines (Y direction) or the direction of dots (X direction), and additively mixing three dots (3 bit data) constituting one dot (pixel) of visible information through display ON or OFF thereof.
Meanwhile, development of multi-color and multi-tone display in accordance with the demand for multi-color display and multi-tone display gave rise to a problem of interface between information processing devices such as between a liquid crystal panel and a personal computer. More specifically, if 4096 colors are to be displayed, signal lines corresponding to 4 bits are required for each of R (red), G (green) and B (blue) so that a total of 12 signal lines are required. Further, if 32768 colors are to be displayed, signal lines corresponding to 5 bits (total of 15 signal lines) are required for each of R, G and B. Increase in the number of signal lines will complicate the interface between e.g. the display panel and the personal computer and give rise to unnecessary radiation. This can be prevented by using analog input signal lines.